Numerous processes for the preparation of fexofenadine are known, inter alia those disclosed in WO 93/21156, WO 97/22344 and WO 97/23213, characterized by a high number of steps. None of the known processes is based on a convergent approach, but on the construction of the molecule introducing the various functional groups step-by-step, starting from α,α-dimethylbenzeneacetic acid. An alternative route is described by Kawai S. et al. in J. Org. Chem. 1994, 59, 2620-2622, but it involves various problems which prevent its industrial application. A key step of the synthetic route is the hydration of the alkyne bond in the carboxymethyl ester of formula (A) to give the respective keto derivative of formula (B).

wherein Ph is a phenyl ring.
Hydration in fact involves formation of by-products, which can hardly be removed from the final product. Furthermore, the process by Kawai S. et al. requires the subsequent purification of the ketone of formula (B) by silica gel chromatography. This technique is unsuited to the production of large amounts of product, thereby making the whole process inapplicable on an industrial scale. The problem of by-products formation was substantially solved by EP 1260505 in which such hydration is carried out by means of a platinum, palladium or ruthenium catalyst, optionally in the presence of ligands. These catalysts are, however, very expensive, and significantly affect the final costs.
In view of this problem, EP 1616861 provides a process for hydrating the alkyne bond by use of a less expensive catalyst based on mercury (II) oxide in a C1-C4 alkanol. According to this process, the formation of difficult to remove by-products is further reduced thereby obtaining the corresponding keto compound in high yields.
The amount of mercuric oxide used in the process, that is already 1/10 of that one used by Kawai S. et al., typically ranges from 2 to 4 molar % referred to the substrate. The use of a mercury catalyst, however, is a problem, as it involves formation of wastes with such a mercury content that their disposal is troublesome; this increases costs and has a remarkable impact on the economy of the whole process.
There is therefore the need for an alternative process for the preparation of fexofenadine, which allows carrying out the hydration of the alkyne to the corresponding keto compound in the pure form, by using lower amounts of mercury while providing high yields.